1. Field of the Invention
The present invention relates to a measuring device, a calculating device, a measurement method, and a method for producing an item, which calculate shape information, such as the dimensions, the tolerance, and the angle, of a measurement object by measuring the measurement object.
2. Description of the Related Art
An image measuring device is a device that measures the dimensions of a measurement object. The image measuring device performs image pickup on a measurement object to obtain an image of the measurement object. Then, the image measuring device detects edges (ends) of the measurement object from data regarding a change in the intensity of the image, and calculates the distance between the detected edges, to measure the dimensions of the measurement object. In the method for detecting the edges from the data regarding a change in the intensity of the image of the entire measurement object, surface texture (surface unevenness) or an inner side of a chamfered portion of the measurement object may be falsely detected as an edge. Therefore, when a range in which the edge detection is performed from the data regarding a change in the intensity of the image (edge detection range) is set within a narrow range of the vicinity of true edges, it is possible to reduce the possibility of a false detection. In an existing measuring device, in order to precisely detect the edges of the measurement object, it is necessary for an operator to determine portions that are thought to be the edges from the image and manually set the edge detection range.
Accordingly, in order to reduce such a troublesome task of the operator, a method in Japanese Patent Laid-Open No. 2012-42324 is proposed. This document proposes a measuring device that binarizes a two-dimensional image of the entire measurement object to extract contour lines (temporary edges), and that automatically sets an edge detection range in the vicinity of the contour lines to more precisely detect the positions of the edges within the range. Japanese Patent No. 4400894 proposes a measuring device that three-dimensionally measures a measurement object and that extracts the edges of the measurement object from three-dimensional point group data of the measurement object.
As mentioned above, in the method for detecting edges from data regarding a change in the intensity of the entire image, portions other than the edges may be falsely detected as the edges. Therefore, in the method discussed in Japanese Patent Laid-Open No. 2012-42324, even if a two-dimensional image of the entire measurement object is binarized when the measurement object has surface texture, contour lines (temporary edges) may be falsely detected where the surface texture is provided. As a result, an edge detection range cannot be properly set afterwards.
In the method discussed in Japanese Patent No. 4400894, since three-dimensional data is used, the influence of surface texture on edge detection is small. However, measurement time and the quantity of three-dimensional point group data are in a trade-off relationship, so that it is practically difficult to obtain three-dimensional point group data having a high resolution (high density). This is because, even if three-dimensional point group data having a high resolution is obtained, it takes a long time to process a large quantity of three-dimensional point group data. In contrast, when three-dimensional point group data having a low resolution is obtained, the precision is reduced. Thus, the positions of the edges cannot be detected with high precision.